Because of the role of purine and pyrimidine nucleotide
metabolism in diseases such as cancer and viral infection, many of the enzymes
involved are targets for drug design. We have focused considerable effort on
nucleoside phosphorylases, which are found in both purine and pyrimidine
pathways.
Purine nucleoside phosphorylase is required for T-cell development. In collaboration
with Professor
Eric
Sorscher,
University of Alabama at Birmingham School of Medicine and Dr. William
Parker, Southern
Research Institute,
we also study bacterial purine nucleoside phosphorylase because of its application
in prodrug activation in the context of gene therapy.

We are
investigating enzymes involved pathways that synthesize, degrade or utilize purines and pyrimidines. Systematic investigation
of an entire
biochemical
pathway
provides
important
clues about
protein evolution. Our current emphasis is on multifunctional enzymes associated with these pathways that had not been previously characterized. We are also particularly interested in the novel activities associated with two newly discovered catabolic pathways: one for each pyrimidines and one for purines. Purine utilization is initiated by a cyclohydrolase reaction. Because many uncharacterized bacterial operons contain cyclohydrolase genes, we are exploring novel biosynthetic pathways for purine derived metabolites. Our primary collaborator in these studies is Professor Tadhg
Begley of Texas A&M.

We are also interested in cofactor biosynthesis. We are
currently focusing our efforts in this area on thiamin and pyridoxal 5'-phosphate (PLP)
biosynthesis. Many of
the reactions catalyzed by the enzymes in thiamin biosynthesis involve unprecedented
chemistry and elucidation of catalytic mechanism is a major goal. By studying
these
enzymes,
we have also discovered interesting evolutionary links to other pathways. PLP is the
biologically active form of vitamin B6 and is an important cofactor for several
of the enzymes involved in the metabolism of amine-containing natural products
such as amino acids and amino-sugars. Of particular evolutionary interest
is the finding that there are two distinct PLP biosynthetic pathways that
have not yet been found to coexist in the same organism. Our primary collaborators
for these studies are Professor Tadhg
Begley of Texas A&M and Dr. Ivo Tews of the University of Southampton.

A recent emphasis is the study of enzymes involved in diphthamide biosynthesis. Diphthamide is a unique posttranslational modification that occurs in all eukaryotes. The biosynthesis of diphthamide requires multiple proteins, and mutations in several of them have been connected to cancer. We plan to study the mechanism of diphthamide biosynthesis and the function of each protein required for the biosynthesis. This will provide important insights into the function of diphthamide, the regulation of diphthamide biosynthesis, and the mechanism of tumor formation in the absence of diphthamide biosynthesis, possibly leading to new ways to treat or prevent cancer. Our primary collaborator for this work is Dr. Hening Lin of Cornell University.

Finally, we are interested in synchrotron radiation and
its application in macromolecular crystallography. Our group lead
an effort
to construct, and is now operating a facility at the Advanced Photon Source, that is designed for the study technically
challenging crystallographic samples. The Northeastern Collaborative Access
Team (NE-CAT), with
Professor Ealick as director, is operating undulator beamlines at Sector
24 of the Advanced
Photon Source (APS) at Argonne National Laboratory in
Argonne, Illinois. Of particular interest to the crystallographic community
are the microdiffractometers that we have deployed for analyzing crystals that are much smaller
than those usually usable and the robotics interface that makes data collection more streamlined. We installed a pixel array detector on the beamline and are making increasing use of remote data collection for the convenience of our users.